Property loss, personal injury and loss of life due to fire can often be minimized or avoided when smoke or heat detectors are employed to provide an alarm during the initial stages of a fire. Consequently, local law in many jurisdictions requires that smoke and heat detectors with alarms be provided in public and commercial buildings and private homes. This has led to the development of a wide variety of commercially available smoke and heat detectors which are battery operated or are connected to the electrical wiring circuit of a building by a permanent wiring connection or by reception in a light socket or other female electrical receptacle.
In general, fire safety experts recommend that smoke alarm detectors be placed near the ceiling of a room and preferably near the center. In older homes, this recommended position is usually occupied by an existing light fixture, and in such cases, removable detector-light combinations of the type shown by U.S. Pat. Nos. 4,694,285 and 4,812,827 to Scripps, 4,717,910 to Scripps et al., and 4,980,672 to Murphy can be threaded into the fixture. In newer homes, there may be no central ceiling fixture in a room, and in such cases, detector alarm devices which incorporate a light fixture have been hard wired into the house circuit and provide a permanently mounted fixture on the ceiling of a room. Since both the permanent and removable detector units incorporate lights, which may be switched on and off by conventional wall switches, such detectors are powered by rechargeable batteries which are charged when the detector light is switched on by a wall switch.
A problem with ceiling mounted detectors powered by rechargeable batteries is that they are difficult to reach and deactivate in the event the alarm is inadvertently triggered by a condition which is not dangerous. For example, cigarette and cooking smoke have the capability to trigger a smoke alarm, as does steam from cooking or a shower, and normally the alarm will remain operative until the alarm triggering condition dissipates. However, it is difficult or impossible, particularly for elderly or infirm persons, to reach ceiling mounted detectors to deactivate an alarm resulting from a false alarm condition.
In the past, attempts have been made to temporarily disable detector alarms in the event that a false alarm condition occurs. U.S. Pat. No. 4,313,110 to Subulak et al. discloses a manually actuated control circuit for temporarily deactivating a smoke alarm and then automatically reactivating the same after a predetermined time delay. However, this device is controlled by a switch activating pull chain which hangs from the detector and which would prove to be unsightly and often difficult to locate at night when attached to a ceiling mounted unit.
U.S. Pat. No. 5,093,651 shows a smoke detector unit having a switch for temporary deactivation of the detector connected on the unit between the battery and the detector component. This switch would be difficult to reach in the case of a ceiling mounted unit.
Finally, U.S. Pat. No. 4,788,530 to Bernier discloses a remote switching device for deactivating a ceiling mounted smoke detector which is affixed to a wall below the detector. This switching device includes a holding relay, a dry cell battery and a time delay circuit, and is connected to the smoke detector by special wiring installed in the wall and ceiling.
Large multistory homes and buildings often have one or more alarm detectors installed on each level, and it is often difficult when an alarm condition occurs on a remote level, for it to be promptly recognized and action taken by persons on other levels. In an attempt to alleviate this problem, U.S. Pat. No. 4,812,827 to Scripps illustrates a detector unit combined with a small radio transmitter which communicates with a second remote detector having a small radio receiver. This system is effective only if the initial alarm condition occurs in the vicinity of the detector with the transmitter. To be even more effective, each detector would have to incorporate both a radio transmitter and a radio receiver, which could prove expensive and result in a bulky and unsightly unit.
Security lighting systems have been developed which utilize the utility power lines of a building to provide communication between a master control transmitting unit and a plurality of remote light receiving units. U.S. Pat. Nos. 5,031,082 to Bierend and 5,072,216 to Grange disclose power line transmitting and receiving systems of this type. Microprocessor transmitters and receivers have also been developed to communicate over the utility power lines of a building to control the operation of an electrical appliance. U.S. Pat. No. 5,189,412 to Mehta et al. discloses a microprocessor control system of this type. Unfortunately, this technology has never been adapted for use with detector sensing systems such as fire, heat and smoke detector.